(1) Field of the Invention
The present invention relates to a proportional solenoid valve control system which is applicable, for example, to hydraulic systems used in heavy equipment, automatic transmission systems, and vehicle fuel injectors.
(2) Description of the Prior Art
A proportional solenoid valve is described in Machine Design, pp. 69-72, February 1983. A new option for hydraulic system control is also described in Machine Design, pp. 77-81, March 1984.
According to the above-identified documents, proportional solenoid valves were developed to fill the gap between servovalves and conventional on/off solenoid valves. An electronically controlled proportional solenoid valve can proportionally control a hydraulic system relative to an on/off solenoid valve, and has a lower cost and simpler control system relative to a servovalve.
In particular, while a servovalve has a minimal deadband, and a faster response time and frequency response, it is five times more expensive than a proportional solenoid valve. An on/off solenoid valve is half the cost of a proportional solenoid valve, however, it can only control the on/off operation of a hydraulic system.
It is desirable that a proportional solenoid valve have a control performance equal to that of a servovalve.
In addition, to reduce power consumption, a pulse width modulation technique is adapted to the driving circuit of the proportional solenoid valve.